Effect of Glass Transition Temperature on the Energy Storage Properties of Nitroxide Radical Containing Polymers

Stable nitroxide radical bearing polymers are attracting much attention for their application as electrode materials in organic radical batteries. These unique redox-active polymeric materials have unusually rapid rates of electron-transfer for non-conjugated polymer systems. This behavior results in unique applications in batteries because of enhanced charging capability and excellent cycling stability of the nitroxide radical functionality. A greater understanding of the inherent charge transfer limitations in such systems, particularly with respect to the relationship between performance and structure of the radical bearing polymer, are paramount to further advancements in the field. While ion transport through neutral polymer networks has been well-studied for solid polymer electrolytes consisting of charged salts incorporated inside a neutral cross-linked polymer matrix, nitroxide radical materials differ dramatically in complexity from typical solid polymer electrolytes. It has been observed that ionic motion in the former systems is coupled with segmental motion of the polymer matrix; hence, ion transport can be correlated with a polymer’s glass transition temperature (T_g). However, the T_g of radical containing polymers is expected to change dramatically and reversibly upon charging and discharging between neutral and cationic states. Therefore, it is essential to evaluate how charge transfer is affected by changes in the energetics of molecular motion. In this work, we conducted a systematic study of a class of nitroxide radical polymers for which the T_g of the materials are systematically tuned either by incorporating butyl acrylate comonomers into the backbone or by incorporating the nitroxide functionality at the terminus of a long alkyl chain. Preliminary synthesis, characterization, spectroscopic, and electrochemical data will be presented.